I read it ages ago when I was still frequenting a certain finance discussion forum (whose name totally evades me now, and I did just try looking up such forums but failed to find it) back in the post 2008 Crash years, hence why the end date in that statistic is 2012.
This is the best I found on the subject. Note that the numbers are quite different from the statistic I quoted since they’re not the same thing (it’s about labour share of income in the whole Economy, rather than the corporate labour to revenue ratio) but you can see the very same trend I mentioned in this report and what’s used there is almost certainly a better statistic to get an overall view of what’s going on.